The present invention relates to high precision measuring methods and apparatus, and particularly to a method and apparatus for measuring distance, temperature, and any other parameter having a known relation to the transmit time of movement of an energy wave through a medium.
Many measuring techniques are known for measuring distance, temperature, and other parameters, but such known techniques generally increase in expense according to the precision desired, and also generally have an upper limit as to the precision practically attainable by the technique. For example, to measure distances of meters or kilometers with a precision of microns or fractions of microns is extremely expensive, if attainable at all. The same limitations apply with respect to measuring temperature and other conditions.
An object of the present invention is to provide a method and apparatus for measuring distances, temperatures, and a number of other parameters, in a manner which can be implemented with relatively low-cost equipment and with a very high degree of precision.
According to one aspect of the present invention, there is provided a method of measuring a predetermined parameter having a known relation to the transit time of movement of an energy wave through a medium, comprising: transmitting from a first location in the medium a cyclically-repeating energy wave; receiving the cyclically-repeating energy wave at a second location in the medium; detecting a predetermined fiducial point in the cyclically-repeating energy wave received at the second location; continuously changing the frequency of transmission of the cyclically-repeating energy wave from the first location to the second location in accordance with the detected fiducial point of each cyclically-repeating energy wave received at the second location such that the number of waves received at the second location from the first location is a whole integer; and utilizing the change in frequency to produce a measurement of the transit time of the energy wave from the first location to the second location, and thereby, a measurement of the predetermined parameter.
As will be described more particularly below, the measurement may be the absolute value of the parameter, or merely the changes in the parameter during the measurement period. The description below sets forth a number of examples of parameters that can be measured with a high degree of precision, including distance, temperature, pressure, gaseous flow velocity, gaseous composition, etc., but it will be appreciated that the invention could be used in many other applications for measuring almost any parameter having a known relation to the transmit time of movement of an energy wave through a medium, or for controlling a system according to the measured parameter. A number of applications of the invention, both in the medical field as well as in the industrial field, are described below for purposes of example.
In most of the applications described below, the cyclically-repeating energy wave transmitted by the transmitter is an acoustical (compressional) wave. However, the invention could also be implemented with electromagnetic waves, particularly in applications requiring the measurement of relatively large distances with a high degree of precision.
Further features and advantages of the invention will be apparent from the description below.